Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $136.53   13.267%   $154.6434   $154.64   $154.65   $154.60  
  Purchase #2 $249.27   11.768%   $278.6041   $278.60   $278.60   $278.60  
  Purchase #3 $179.81   11.154%   $199.866   $199.87   $199.85   $199.90  
  Purchase #4 $204.25   8.546%   $221.7052   $221.71   $221.70   $221.70  
  Purchase #5 $182.28   3.633%   $188.9022   $188.90   $188.90   $188.90  
  Purchase #6 $21.62   4.668%   $22.6292   $22.63   $22.65   $22.60  
  Purchase #7 $160.77   3.255%   $166.0031   $166.00   $166.00   $166.00  
  7 purchase totals = $1,134.53       $1,232.3532   $1,232.35   $1,232.35   $1,232.30